JPS588714A - Recovery of washing solvent - Google Patents

Abstract

PURPOSE:To recover a purified solvent in a high yield by evaporating a washing solvent used for washing the production apparatus of an aromatic vinyl/acrylonitrile copolymer thereby separating a solvent/monomer mixture from a polymeric substance and distilling the former together with water to form a water/ monomer azeotrope. CONSTITUTION:A styrene/acrylonitrile copolymer is produced by bulk polymerization. After withdrawing the polymerized solution, a polymerization apparatus 2 is filled and washed with a solvent supplied from a tank 1 and selected from the group consisting of dimethylformamide, dimethylacetamide and dimethyl sulfoxide. The washing solvent containing the washed monomer and polymer substance is continuously transferred by a pump 4 through a tank 3 to an evaporator 4, wherein a vapor comprising the monomer and the solvent is separated from the polymeric substance. In a distillation tower, the former is further distilled together with water introduced from a tank 11, whereby the monomer and the water are azeotropically distilled to recover a purified solvent 13. The monomer/water azeotrope is passed through a condenser 10 to the tank 11, wherein the azeotrope separated into a water phase and a monomer phase and the former is recirculated into the tower 8.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for regenerating and recovering a solvent used for cleaning equipment for producing an aromatic vinyl-acrylonitrile copolymer.

It is known that during the production of aromatic vinyl-acrylonitrile copolymers, polymeric substances that are insoluble or sparingly soluble in monomers and polymerization solvents are produced in production equipment. This polymer substance adheres to the inside of the reaction tank and heat transfer equipment, causing a decrease in heat transfer performance in the manufacturing equipment and clogging of piping. This results in a decrease in reaction controllability and a decrease in productivity, which is a major obstacle to stable operation. Furthermore, a part of the polymer substance is mixed into the product, resulting in deterioration of the product appearance and color.

For this reason, it was necessary to stop the operation at an appropriate time and remove this polymeric substance.

As a method for removing this polymer substance, manual removal work is also carried out, but it requires a lot of manpower and time, and it also causes damage to the equipment and contamination by residual chemical substances from the operator, so this is the preferred method. It can not be said.

A method of peeling and removing using high-pressure fluid is also known, but this cannot be applied if there are locations where high-pressure fluid cannot be directly sprayed due to the structure of the device, or if the strength is insufficient.

For this reason, a cleaning removal method using a solvent is generally used. When cleaning with a monomer, a solvent obtained by dissolving the polymer is used because the dissolving ability is poor at low temperatures and the cleaning effect is small at high temperatures due to concerns about polymerization of the monomer. Argyl amide such as dimethylformamide and argyl sulfoxide such as dimethyl sulfoxide are good solvents for aromatic vinyl-acrylonitrile copolymers, but if they are used for cleaning and monomers etc. are mixed in, the polymer substances may be It is known that the dissolution ability decreases.

This polymer material is swelled with monomers such as aromatic vinyl-acrylonitrile copolymer.1. in a state of
It itself contains many monomers. Therefore, when this polymeric substance is washed fI using a solvent, the monomer is mixed into the solvent, reducing the cleaning power. The ability to clean polymeric substances may reach its limit with one cleaning. For example, when a styrene-acrylonitrile copolymer is produced by continuous bulk polymerization, a large amount of polymer 71 and lj polymers are present in the polymerization apparatus at the end of polymerization, so it is necessary to wash the copolymer in batches using a washing solvent. In this case, the concentration of the monomer, etc. in the solvent is λ~,
20% by weight, usually reaching 72% by weight, making it inappropriate to use the residue for washing again, and it is necessary to recover and purify 1jli% J+ solvent. In order to prevent an increase in the concentration of monomers, etc. in the cleaning solvent, the interior of the polymerization apparatus may be dried to remove the monomers, but this requires a long drying time and is difficult to operate. This is often a problem for the following reasons.

Generally, solvents used for cleaning are expensive and therefore need to be recovered and reused. However, in order to recover the solvent, it is necessary to separate the polymer substance and the monomer, and filtration or absorption methods cannot be used. For this reason, it is generally carried out by a distillation operation, but since it contains polymeric substances, a method is adopted in which the cleaning solvent and monomer are fractionally distilled in a batch manner, and then the polymeric substances are separated.

However, batch-type distillation operations have drawbacks such as a large amount of solvent loss during monomer fractionation, being labor-intensive, and the need for larger equipment and higher equipment costs if large quantities need to be processed. many.

Therefore, the present inventors conducted intensive research on efficient implementation of solvent cleaning of aromatic vinyl-acrylonitrile copolymer manufacturing equipment and recovery of the solvent, and found that aromatic vinyl We have completed a method for recovering cleaning solvents from equipment for producing zacrylonitrile copolymer.

The present invention uses a cleaning solvent mainly composed of one selected from the group consisting of dimethylformamide, dimethylacetamide, and dimethyl sulfoxide to remove polymeric substances adhering to an apparatus for producing an aromatic vinyl-acrylonitrile copolymer. In recovering the washing solvent from the solvent containing polymeric substances and monomers produced as a result of washing, (a) continuously introducing the solvent into an evaporator; (b)
) Evaporating the cleaning solvent and monomer in the evaporator to separate the polymeric substance contained in the solvent; (C) converting the mixture of the cleaning solvent and monomer evaporated from the evaporator into vapor; (1) At the same time, water is supplied into the distillation column, and a fraction containing an azeotrope of water and a monomer as a main component is distilled from the top of the column; (e) the fraction is Separating into a phase mainly composed of water and a phase mainly composed of monomers, (1) using part or all of the phase mainly composed of water as water in (C1), (g) A cleaning solvent recovery method is characterized in that the purified cleaning solvent is recovered from the bottom of the column.

The aromatic vinyl-acrylonitrile copolymer to which the present invention can be applied preferably has acrylonitrile of 1 to 10S.
A copolymer having a weight coefficient of O, more preferably 20 to 0, and may also contain a nitrile monomer such as methacrylonitrile instead of acrylonitrile. Examples of the aromatic vinyl monomer include styrene, α -Methylstyrene and the like. Copolymers can be produced by any method such as suspension polymerization, solution polymerization, and bulk polymerization, but especially in solution polymerization and bulk polymerization, the polymer substances attached to the polymerization equipment are monomers, etc. Since it is in a swollen state, the effect of applying the present invention is great. The monomers that make this aromatic vinyl-acrylonitrile copolymer are monomers such as acrylonitrile, methacrylonitrile, styrene, and α-methylstyrene, which form an azeotropic mixture with water and are difficult to dissolve in water. It is also used as a polymerization solvent in Copolymerization 11.11. Solvents that form an azeotrope with water and are difficult to dissolve in water, such as benzene, toluene, xylene, ethylbenzene, hegyzane, and heptane. It may also include.

The filter washing solvent used in the present invention is dimethylpolamide,
It contains seven types selected from the group consisting of dimethylacetamide and dimethylsulfoxide as main components, and dimethylpolamide is suitable for the styrene-acryloni I/lyl copolymer.

The wash solvent containing polymeric substances and monomers resulting from the wash is introduced into an evaporator capable of continuously evaporating the solvent. As the evaporation device, a flash evaporator, a thin film evaporator, a container, etc. can be used, and it is also possible to emit 411.4 Jl of the polymeric substance. This operation can be carried out under pressure, atmospheric pressure or reduced pressure, but rather than at atmospheric pressure, which is easier to operate, the vapor is introduced into a distillation column in order to separate the solvent and monomer. As a distillation column, a packed column or a tray column is usually used, and fractional distillation is carried out under atmospheric pressure or reduced pressure. For this fractional distillation, a number of plates in the distillation column of 7 to 20 is sufficient. It is advantageous to feed the mixed vapor of solvent and monomer between the bottom of the column and the middle stage, usually several stages below the middle stage.

This distillation column is supplied with water for monomer removal. The distillate whose main component is an azeotropic mixture of water and monomer distilled from the top of the column is separated into a phase whose main component is monomer and a phase whose main component is water. A stationary divided tank is usually used for this operation, and by constantly using part or all of the separated water-based phase for reflux, it is possible to use water in a closed system. Water is normally supplied by a method in which water is prepared in advance in a static separation tank before the start of the distillation operation and used for reflux, or by a method in which water or steam is introduced into the distillation column. It is also possible to supply water when introducing the washing solvent into the evaporator.

The phase mainly composed of monomers separated by standing is removed by continuous or batch extraction.

At the bottom of the distillation column, heating devices such as a steam jacket and reboiler are installed for rectification.

Is the purified washing solvent collected from the bottom of the column and stored?
Alternatively, it is resupplied to the manufacturing equipment for cleaning.

When the present invention is applied to nuthylene-acrylonitrile J1, dimethylpormamide used for cleaning polymer production equipment, dimethylpolamide with purity exceeding 99% by weight is recovered at a recovery rate of 1-1-1% by weight or more than 95% by weight. It is possible.

According to the method of the invention aromatic vinyl-acryloni) I
Washing of the production equipment for J-ru copolymer using f-IF/9
1: The purified solvent can be effectively recovered.

By continuously recovering the washing solvent, monomers and the like can be removed efficiently and the recovery rate of the solvent is also high. Furthermore, by supplying the recovered solvent to the polymerization apparatus again, it is possible to shorten the cleaning time and at the same time reduce the cost and the amount of solvent required.

Hereinafter, the present invention will be explained by way of examples with reference to FIG. 7.

Example: Continuous production of styrene-acrylonitrile copolymer (containing acrylonitrile in a weight ratio of 211%) using a bulk polymerization method.
2 E1 implementation 1~, content amount 3 with attached product molecular substance
The polymerization apparatus λ of m' was washed with dimethylpolamide.

After the bulk polymerization is completed, the polymerization liquid is discharged from the polymerization apparatus. At this time, the polymeric substance adhering to the inside of the apparatus is in a swollen state due to the monomers acrylonitrile and styrene and the ethylbenzene used as the polymerization solvent.

Dimethylpolamide was supplied from the supply tank to this polymerization apparatus until it became full, and the temperature was raised to 730°C while stirring the inside of the polymerization apparatus.
Washed for 70 hours. After the cleaning was completed, the solvent used for cleaning contained monomers and the like in the weight range and polymeric substances in the weight range. The solvent used for this cleaning passes through the relay tank 3 and is continuously sent to the evaporator S by a pump tank.

This evaporator is a gool heating tank: it is equipped with a steam and heat medium jacket capable of heating up to 130°C and an internal coil. A gear pump O is attached to the bottom of the evaporator to discharge the polymeric substance. In addition, 300 n1 is placed at the top of the heating tank to prevent entrainment of polymer droplets.
A filling section 7 with a height of 11 is provided. The evaporation operation is carried out under atmospheric pressure (105 atm), the evaporator is maintained at /15°C, and the vapor generated here is sent to the distillation column g at a rate of 2701 g/'nr.

This distillation column was a packed column with a column diameter of 1 I-3 Omrn, and had a total of 7 columns, 1 stage above the steam supply section and 3 stages below the steam supply section. This distillation column includes a glue boiler 7 for heating the bottom liquid, a condenser 10 for top steam, and a separation tank for condensed liquid (capacity 1
000e) and a reflux pump/2 are attached.

′ At the top of the fractionation column, the water prepared in the separation tank is refluxed to separate the water and the solvent. The l'L-mer etc. are made to be dI'.

At this time, the single 111' compound and the like that azeotroped and came out from the top of the column are separated in a liquid separation tank and the aqueous layer is used for reflux. Reflux ratio R at this time
The tension was 0. In this operation, most of the 1:srlt polymer is removed from the bottom of the fractionation column. Dimethylpolamide was obtained in 97 cities. This dimethylformamide/
3 was collected in a storage tank.

Through this recovery operation, 9 g of dimethylformamide was recovered.

[Brief explanation of the drawing]

FIG. 1 is an example of a flow sheet of an apparatus used to carry out the present invention. /: Solvent supply tank,! : Polymerization device 3: Relay tank Il, : Pump S: Evaporator B: Gabon pump 7: Filling section g: Distillation column'? : Reboiler 10: Condenser //: Separation tank /2 = Reflux pump /3: Storage tank
M: Motor agent Tadashi Wakabayashi Figure 1

Claims (1)

[Scope of Claims] / A method for cleaning polymeric substances adhering to equipment for producing aromatic vinyl-acrylonitrile copolymers, the main component of which is one selected from the group consisting of dimethylpolamide, dimethylacetamide, and dimethylsulfoxide. When washing and removing a solvent and recovering the washing solvent from the solvent containing polymeric substances and monomers produced as a result of washing, (a) the solvent is continuously introduced into an evaporator; (b)
) In the evaporator/! Evaporating the IL cleaning solvent and monomer to separate the polymeric substance contained in the solvent; (C) supplying the mixture of the cleaning solvent and monomer evaporated from the evaporator to the distillation column as vapor; (C1) At the same time, water is supplied into the distillation column, and a fraction containing an azeotrope of water and a monomer as a main component is distilled from the top of the column; 4) Separate the phase and 1' into a phase whose main component is mercury, (b) Use water as part or all of the main component and the mer phase (d), (g) At the bottom of the tower. Claim 1, characterized in that the cleaning solvent is recovered from a purified washing solvent. 3. The method according to claim 1, wherein the monomers are acrylonitrile and nutylene." A method according to claim 1, comprising a hydrocarbon azeotropic with.